This invention relates to the field of manufacturing microelectronic devices, more particularly to the wafer cleaning and drying processes needed before the epitaxial deposition step.
In the manufacture of advanced ULSI integrated circuit (IC) microelectronic devices, which have dimensions in the low nanometer (nm) range, pre-epitaxial (pre-epi) cleaning procedures play critically important role. Such pre-epi processes can be either non-aqueous, or aqueous. In IC manufacturing, wafers are typically mixed with oxide wafers or the wafers are patterned. Typically, exposed silicon is adjacent to oxide or nitride areas. In HF solutions, etch byproducts will be transported from the hydrophilic surface to hydrophobic surfaces. This results in high particles counts on the exposed silicon.
Carter et al, U.S. Pat. No. 6,221,168, discloses a gas phase, non-aqueous pre-epi process for treating such microelectronic substrates which uses hydrogen fluoride (HF), isopropyl alcohol (IPA), and nitrogen (N2) at a pressure of 125 to 175 torr, and in a narrow ratio of HF, IPA, and N2, with temperature controlled by infra-red or UV lamps.
Kashkoush, et al, In-Situ Chemical Concentration Control for Wafer Wet Cleaning, Mat. Res. Soc. Symp. Proc. Vol. 477, 311-316, disclose an “RCA” type aqueous pre-epi process which includes an SC1 (Standard Clean 1) step for removing particles and an SC2 (Standard Clean 2) step to remove metals. SCI comprises 1 part 28% NH4OH, 1 part 30% H2O2, and 5 parts H2O, by weight, C. for 10 minutes. SC2 is 1 part 37% HC1, 1 part 30% H2O2, and 6 parts H2O), by weight. HF mix (HFM) is a dilute HF process, wherein the ratio of HF to H2O) is about 200-100:1. Other mix ratios were also discussed. Chemical concentration was controlled by continually monitoring the conductivity by means of in-line sensors.
Patruno, et al, In-Situ Rinse HF-Last for Pre-Epitaxy Cleaning, UCPSS '94, pp. 247-250, and HF-In-Situ Tank used in HF-Last Cleaning [ECS' 94, pp. 195-205] teach dilute HF mixture being used as a final step in pre-epi cleaning, known as “HF-last,” with a special, dedicated in-situ HF last rinse tank in an automated wet bench apparatus wherein a diluted HF solution is displaced by DI water. After the rinse step, the silicon wafers are transferred to a final rinse tank and then to an IPA dryer. Such multiple tank process is known in the art as SC1/Rinse/HF/Rinse/Dry.
However, prior art multi-tank HF processes result in high particle counts at 0.12 μm (>10,000). Consequently, post epitaxial defects are also high (>30 000). These light point defects (LPDs) are considered to be nucleation sites during subsequent epitaxial deposition. In the prior art, wafer transfer between tanks plays a significant role of increasing the silicate deposition into silicon wafers.
Verhaverbeke, Isothermal Epi-Si Deposition at 800° C., Electrochemical Society Proceedings, Vol. 99-36, 445-451, discloses an HF-last cleaning sequence for a short H2 pre-epi process wherein SOM-HF, SC1-HF, HF only, and HF/HCl are compared, and wherein HF last is taught to lower the bake/deposition temperature to substantially below 1070 C. IPA dry using the CFM Technologies, Inc., Direct Displace™ method wherein large volumes of IPA are introduced to replace the rinse water or the HF solution itself, i.e., the IPA dry step is conducted without any rinse after the HF etch step. Average particles precount >0.16 μm were 32 and average delta was 1.32+/−7, with the highest delta being 12 particles added.
It is an object of the present invention to reduce the particle counts in an aqueous HF process for cleaning integrated circuits significantly below previously reported levels and at a tighter. Another object of the present invention is provide improved silicon wafer cleaning methods and cleaning apparatus which will reduce post epitaxial defects in the manufacture of such integrated circuits.